The title compound, [Co(C5H3N2O2)2(H2O)2]·2H2O, contains a Co(II) ion on an inversion center, exhibiting an octa-hedral coordination geometry. The equatorial plane is formed by two trans-related N,O-bidentate pyridazine-3-carboxyl-ate ligands and the axial positions are occupied by two water mol-ecules. The Co(II) complex mol-ecules are stacked in a column along the a-axis direction by an O-H⋯N hydrogen bond between the non-coordinating pyridazine N atom and the coordinating water mol-ecule. These columns are further connected into a layer parallel to the ac plane by additional hydrogen bonds involving the coordinating and non-coordinating water mol-ecules, and the non-coordinating carboxyl-ate O atom. The crystal packing is completed by inter-layer weak C-H⋯O inter-actions.